Altering Dendrimer Structure of Fibrous-Silica-HZSM5 for Enhanced Product Selectivity of Benzene Methylation

Dendrimeric fibrous silica HZSM-5 (HFSZ) catalysts were prepared using a microemulsion technique and ZSM-5-seeding crystallization with different oil phases, benzene, toluene, and xylene, and denoted as FB, FT, and FX, respectively. The HFSZ catalysts possessed a well ordered crystalline structure with chestnut-like spherical particles, rich with dendrimeric fiber morphology. It was found that the hydrophobicity of the oil phase significantly affected the physicochemical properties of the HFSZ catalysts that altered their activity toward benzene methylation. The density of dendrimeric fibers and ensuing acidities were found to play crucial roles in enhancing the selective production of toluene and p-xylene via transalkylation and dealkylation of bulkier aromatics. The production of ethylbenzene (EB) using commercial HZSM-5 could be suppressed to give major products of toluene (84%) and p-xylene (58%) when using FB and FX at 673 and 623 K, respectively.